I have gone through this same transition that you have. Started with barrel evaporator last year and was getting a max of 2.5gph with 40 taps. Upgraded to a block arch this year and can get as high as 8gph with 80 taps (4 steam pans). The block arch is removable and relatively inexpensive. I lined the inside of the arch with fire brick, but did not mortar the bricks (I welded an internal frame to hold the bricks in the firebox area), so that I could reuse the bricks in the future for a steel evaporator. Gasketing the pans with a proper fiber blanket is key to low ash, as well as letting the fire die down to coals only.
I added a blower to the block arch under the door and this cut down on the amount of ash and coals I had at the end of each burn run by about 80 percent.
2015- Didn't know my new property enough to tap anything. 4-feet of snow on the ground.
2016- 41 Taps with home made barrel evaporator. Made 1.5 gallons syrup.
2017- 79 Taps with home made block arch evaporator. Syrup still to come.